The present invention relates to an apparatus for development and fixation of dyes on a printed textile sheet by appplication of microwaves, and more particularly relates to improvement in continuous aftertreatment of a printed textile sheet under emanation of microwaves for uniform and ideal colour fixation and development.
Colour fixation and development on a textile sheet has long been carried out by firstly passing the textile sheet through a dryer and, thereafter, subjecting same to steam heating.
For aftertreatment of a dyed textile sheet in general, it was already proposed to subject the dyed textile sheet to emanation of microwaves in wet state. Here the term "microwaves" refers to electro-magnetic waves having frequencies in a range from 300 to 30,000 MHz.
Microwaves have a wide variety of advantages particular when used for treatment of a textile sheet in wet state. First, they permeate into and heat the textile sheet very swiftly. Secondly, they can be selectively absorbed in an object with large dielectric loss and heat only necessary sections of the object, since their heat generation is caused by dielectric loss. There is almost no heating of unnecessary sections of the object, thereby well avoiding extravagance of thermal energy generated by microwave emanation. Thirdly, when an object is exposed to microwaves, the object also generates heat by itself and such heat naturally raises the temperature of the ambient atmosphere. As a consequence, the amount of the thermal energy otherwise needed for heating the ambient atmosphere for the treatment can be greatly reduced. Fourthly, microwaves usually cause almost simultaneous temperature rise at different sections of an object exposed to them. As a consequence, regional variation in temperature within the object can be significantly minimized and this leads to ideal and uniform heating of the object. Finally, heating condition can easily and swiftly controlled in accordance with demands in the actual treatment merely by adjusting the output voltage for microwave generation.
Emanation of microwaves onto a textile sheet causes ionic conduction and dipole rotation of the fibrous materials composing the textile sheet, water and aqueous agents contained in the textile sheet. This is believed to results in swift and uniform heating of the textile sheet exposed to microwaves.
Based on recognition of these advantages, various systems have been proposed in the field of textile treatment. One example of such proposals is disclosed in U.S. Pat. No. 4,274,209 (EPC patent application No. 79850116.9) filed by the inventor (applicant) of the present invention on Dec. 28, 1979. In the case of this proposed system, a textile sheet in the form of a roll is placed within a confined chamber replete with saturated or overheated steam, and rotated under concurrent emanation of microwaves.
This proposed system well makes use of the advantages inherent to microwaves. However, since the textile sheet in this system is exposed to steam and microwaves in the form of a roll, there is a significant difference in treatment effect between the section of the textile sheet close to the core of the roll and the section close to the periphery of the roll, since steam and microwaves both have easier access to the peripheral sections of the roll. As a consequence, one cannot expect uniform treatment effect over the entire length of the textile sheet.
In order to remove this disadvantage, a more dynamic system has also been proposed by the inventor of the present invention. In accordance with this dynamic system, a pair of rolls of a textile sheet are placed within a confined chamber replete with saturated or overheated steam, and the textile sheet is continually transferred from one roll to another and vice versa under concurrent emanation of microwaves.
This improved system well solves the uniformity problem. However, since the textile sheet has to be kept, even provisionally, within the confined chamber during the treatment, this system is applicable to the so-called batch process only. In other words, this system is quite unsuited for any continuous textile process in which a textile sheet has to be continually transferred from station to station.
In addition, when a printed textile sheet is subjected to any aftertreatment, it is preferred that at least the printed surface of the textile sheet should stay out of any contact with other objects such as guide rollers untill colour fixation and development are finalized. From this point of view, it is rather undesirable to prepare the textile sheet in a roll form before emanation of microwaves. It is well known in the art that temperature and moisture condition of a printed textile sheet pose delicate influence on its dye development and fixation by microwave emanation. Colour size spots are usually printed on the textile sheet with time phase during printing process and such time-phased printing of colour size spots is apt to cause moisture variation over the entire area of the textile sheet. Variation in moisture and temperature further poses serious influence on thermal effect of microwave emanation. So, for ideal development and fixation of dyes, the moisture content of the textile sheet needs to be equalized over the entire area before exposure to microwaves. It is also well known that variation in moisture content of a textile sheet is greatly swayed by presence of tension in the textile sheet. In order to remove this variation, it is preferable to advance the textile sheet with minimum tension through the treatment chamber.